The present invention relates to devices for achieving spinal correction, in particular, mechanisms for urging a spinal rod into an implant adapted to receive a rod. While the present invention was developed for use in spinal surgery, it may have uses in other areas of medicine as well.
In many applications, particularly those relating to spinal correction techniques, it is desirable to place a series of implants in a patient's spine prior to inserting a longitudinal member (a rod or a plate) along the spine to interconnect the previously placed implants. On occasion, implants may be vertically spaced from the rod or plate and require a mechanical mechanism to bring the rod or plate into contact with the implant. In the instance of a plate, often the implant is a double threaded bolt with a series of bone screw threads anchoring into the bone and a machine threaded post extending through an opening in the plate. A machine threaded nut slightly larger than the opening in the plate may then be threaded onto the threaded post and tightened to bring the implant closer to the plate. For rod systems, a similar arrangement can be utilized whereby the threaded post of the implant extends through a connector attached to the rod. In these systems a nut is used to draw the implant closer to the connector by progressively threading the nut onto the post of the bone bolt.
Alternatively, it is known to provide a rod introducer mechanism that forces the rod and an implant towards each other. In many cases the implant, either a bone screw or spinal hook, includes an open channel to receive the rod. A plug or set screw can be used to close the channel and lock the rod to the implant. In certain surgical techniques a rod is anchored at both ends by at least one implant, resulting in the rod being suspended above a second implant. A mechanism is then required to urge the second implant and rod together to permit connection of the implant to the rod and more particularly to seat the rod within the open channel of the implant. One such instrument marketed by Sofamor Danek Group as part of the Compact CD.TM. system, is an introducer lever C-6903 which resembles a fork with a pair of offset tines. The tines of this device extend over the vertically spaced rod and under either side of an enlarged portion of the implant. Once in place, the fork handle is moved toward the rod thereby forcing the rod and implant together. One problem with this arrangement is that the fork tines must pass between the implant and the bone, which in many cases may be difficult and may result in damage to the bone. Moreover, the connection between the fork tines and the implant is not a secure engagement and may result in the rod introducer slipping during the procedure of forcing the rod into the implant.
Other types of rod introduction devices have overcome the problems associated with the simple fork device by first achieving a secure attachment to the implant with articulated forceps or the like. Various instruments for gripping and handling implants are commonly known. One such instrument has a pair of articulating branches defining a gripping nose opposite a pair of handles. While many varieties of these forceps exist to accomplish various functions during surgery, some are adapted specifically to securely hold an implant, and in particular, a spinal osteosynthesis implant. The gripping nose of one such configuration utilizes a pair of inwardly facing cylindrical projections disposed at the distal end of the gripping nose. The cylindrical projections are adapted to engage corresponding recesses on an implant, thereby providing a secure grip. Because of the small size of many spinal implants and the accompanying difficulty gaining a secure grip with only manual pressure, such forceps are often utilized in the manipulation and placement of the implants.
In addition to providing a nose for gripping implants, many forceps also provide a locking mechanism to hold the forceps in the gripping position once the implant is gripped. A common example is the provision of one half of a ratchet rack on one articulating branch aligned to engage a second half of the ratchet rack on the other articulating branch. Upon movement of the branches towards one another, the separate halves of the ratchet rack come into engagement thereby preventing separation of the articulating branches. As is common with such arrangements, the articulating branches have sufficient flexibility that they may be flexed with respect to one another, thereby disengaging the ratchet racks.
An alternative forcep locking mechanism is disclosed in U.S. Pat. No. 5,423,855 owned by the Sofamor SNC subsidiary of Sofamor Danek Group. This patent shows forceps having an implant gripping nose as previously discussed. In this configuration, the articulating branches are held in the closed position by a spring biased cap disposed on the end of the branches opposite the gripping nose.
In prior systems, once a secure engagement has been accomplished between the forceps and the implant, a separate apparatus is attached between the forceps and the rod. In one such mechanism marketed by Sofamor Danek Group as the TSRH.TM. mini-corkscrew, a threaded rod is threadedly coupled at one end to the forceps and the other end engages the rod. Rotation of the threaded rod urges the rod and implant towards each other. In another mechanism marketed by Sofamor Danek Group as an articulated rod pusher C-6211 for use with the Compact CD.TM. system, forceps grip the implant and a pivoting two piece rod pusher lever is used to urge the rod and implant towards one another. In this device, a lower end of the first member of the rod pusher engages the rod and the upper end of the first member is pivotally attached to the second member of the rod pusher lever. The lower end of a second member engages the forceps while the upper end of the second member is rotated to force the rod and implant towards each other.
It should be understood that in the various devices described, the implant may move toward the rod, the rod may move or bend toward the implant, or both devices may move towards each other to accomplish the connection. The device which moves depends in large measure on the procedure being performed and the flexibility of the rod utilized. Regardless, each of the prior art mechanisms requires both a device to securely grip the implant and a separate mechanism to apply force to the rod and thereby urge it into the implant. There remains a need for a simple and effective device that accomplishes the desired features of gripping the implant and forcing the rod into the implant.
The present invention overcomes the problems associated with the prior art by providing a gripping mechanism and a rod introduction lever in a single convenient instrument.